This invention relates to the wear of articles, and articles such as those used in manufacturing tooling, and, more particularly, to the evaluation of the extent of wear of such articles without the use of instruments.
Many metallic articles are formed to their final shapes and sizes by metal working techniques utilizing tooling to aid in the forming. In one such technique, a thin metal article is formed from a sheet or coiled strip metal workpiece using a metal forming die. The die is another piece of material having a preselected shape that aids in the forming of the workpiece into its intermediate or final shape. Sheet workpieces are commonly formed by forcing the sheet into a female die using a male die.
Some of the die forming operations involve large tonnages of metal workpieces and produce familiar products. For example, most automobiles have metallic body panels. To fabricate those panels, flat pieces of metal sheet are formed by placing the starting sheet over a female die, and then forcing the sheet into the female die with an appropriately shaped male die. The resulting part has the complex shape of the body panel.
The useful life of tooling such as dies is normally limited by wear that causes changes in their dimensions and thence to the dimensions of the finished parts. As each part is formed, the frictional contact between the sheet workpiece and the tool removes some small amount of material from the tool. Eventually, the tool is so changed in dimension that the final products do not meet the standards. At that point the tool must either be discarded or refurbished.
Evaluation of the extent of wear of tooling is usually accomplished by periodically measuring the dimensions of either the finished part or of the tool itself. It is normally not practical to measure every finished part and/or to measure the tooling after each part is formed, because the measurements would slow the production operation too greatly. For example, if a contoured automobile body panel having a surface area of on the order of 10 square feet is formed between dies, hundreds of dimensional measurements might be required to check whether each dimension of the part is within tolerance as the part emerges from the forming press. Similarly, hundreds of measurements could be required to check the dies to be certain that they are within tolerance.
Another approach is to check the dimensions of the part and/or the tooling periodically, and that is the approach normally taken. If, for example, at one measurement of a formed part all dimensions are within tolerance, then perhaps another ten thousand parts might be formed prior to again measuring the article or the tooling. If at the next measurement there is an unacceptable dimensional variation, then the parts produced since the last inspection would be individually inspected and those not meeting tolerances would be discarded. This procedure can result in scrapping substantial numbers of parts in the event that the loss of tolerances occurred soon after the prior inspection.
In those instances where the tooling itself is to be measured, the measurement process may be slow and cumbersome. The dimensions are typically measured using a micrometer or an automated coordinate-measuring machine. As an example of the time involved, about 6 hours is required to check all of the dimensions of an automobile engine manifold tooling set. The inspection is scheduled after every 10,000 parts formed. From these measurements, retention of dimensions and patterns of wear are evaluated. If the dimensions are no longer within tolerances, then the tooling must be discarded or refurbished.
There is a need for a better approach to evaluation of the extent of tool wear. Desirably, such an approach would be faster, less expensive, and therefore capable of practice more often than existing techniques. The present invention fulfills this need, and further provides related advantages.